Polytetrafluoroethylene (hereinafter "PTFE") has excellent heat resistance, chemical resistance, insulation resistance, non-adhesiveness and self-lubrication. This polymer has found wide use in medical, industrial and recreational fields.
A recent invention (U.S. Pat. No. 3,953,566) provides a process for manufacturing highly porous, yet high strength, shaped, PTFE articles. This process involves blending highly crystalline, fine powder PTFE with a liquid lubricant, extruding this mixture through a die which may have desired cross-sectional configuration, and subsequently expanding the shaped article in one or more directions at rates in excess of 10% per second.
Products produced by this process have found widespread acceptance in the industrial, medical, electrical, and clothing arts. The process is somewhat limited in that it is not readily adaptable to the production of large articles with complex cross-sections. A need for such articles is found, for example, in the industrial filtration arts and in large vessel vascular surgery. Although large composite articles can be manufactured by joining smaller articles together by such conventional methods as sewing, welding or gluing, such articles have a discontinuity at the seam. While in many applications this does not present any severe problems, in others such as filtration and body part replacement, it is extremely important that the structure be as uniform as possible over the entire article. If welding or gluing is used to produce large articles, a dense non-porous area is produced. On the other hand, sewing may produce areas which have a greater porosity than the rest of the article. It has been found that the microstructure of nodes and fibrils present in products produced by U.S. Pat. No. 3,953,566 is particularly desirable as both a filter media and as surface for contacting blood and other body fluids. It would, therefore, be desirable to produce composite, complex shapes by joining articles of expanded PTFE with this microstructure in such a manner that the microstructure remains virtually uninterrupted across the join or seam.